Why should they have been told? A war warning means war is likely immenent doesn't it? That much was pretty clear to everyone. Indeed Short specifically took measure to protect against sabotage which is the kind of attack he expected. Again there was no need to. No they didn't need that information to understand the above. Wrong, still. There was evidence but hardly a mountain. Most of the Magic intercepts as has been pointed out were not translated until well after the fact. Then there was the general consensus in any case that war was coming. In The First Team very early on it makes the point that Halsey was scouting ahead of Enterprise (i.e. to the west) even though he didn't expect the Japanese to be operating East of Wake. War was expected. Kimmel expected it. Short Expected it. Halsey expected it. The list goes on. What no one really expected was for it to start with a carrier raid on PH. A surprise attack yes but not on Pearl. ... What ultimatum? They had already recieved war warnings, what more should have been necessary.